A motor has been known in which a rotor having a permanent magnet, which is fixed to an outer peripheral face of a rotor shaft, is disposed on an inner side of an ring-shaped stator. In this motor, unless the rotor shaft is urged in a thrust direction, when the rotor shaft is rotated, the rotor shaft wobbles in the thrust direction to cause wear to occur in a radial bearing and a noise to generate.
In order to solve the above-mentioned problems, following structures have been known. For example, in a motor in which a U-shaped mounting plate is fixed to an end face on an output side of a stator, an end portion on an opposite output side of a rotor is urged in an output side by a flat spring and a shaft end on the output side of rotor shaft is supported with a bag shaped bearing that is fixed to an end portion of the mounting plate. Alternatively, a rotor shaft is urged on an output side by a coil spring which is disposed between a stepped portion of the rotor shaft and an end face on the output side of a stator, and a shaft end on the output side of the rotor shaft is supported by a bag shaped bearing which is fixed to an end portion of a mounting plate (see, for example, Japanese Patent Laid-Open No. 2005-20857).
However, in the structure disclosed in the above patent reference, the rotor shaft is urged on the output side and the shaft end on the output side of the rotor shaft is supported in a thrust direction. Therefore, the structure can be employed, for example, in the case that a U-shaped mounting plate is fixed to an end face on the output side of the stator like a motor in which a feed screw is formed on the rotor shaft, or in the case that an equipment on which a motor is mounted is provided with a portion for supporting a shaft end on the output side of a rotor shaft. In other words, this structure can be applied only to a case where a shaft end on the output side of a rotor shaft is capable of being supported and thus its application is limited.
Further, in the motor disclosed in the above-mentioned patent reference, when an urging force is applied to a carriage in an output side direction in order to prevent a backlash between a feed screw and the carriage, both of an urging force for preventing the rotor shaft from shaking in a thrust direction and an urging force for preventing the backlash are applied to a portion which supports the shaft end on the output side of the rotor shaft in the thrust direction and thus a large torque loss occurs.
Alternatively, in the case that a rotor shaft is urged toward an opposite output side (opposite side with respect to output side), in a conventional motor, an end face on the opposite output side of the rotor is required to be supported by an end face on the output side of a radial bearing which supports the rotor shaft on an opposite output side. According to the structure described above, since the end face on the opposite output side of the rotor face-contacts with the end face on the output side of the radial bearing, torque loss is large.